Control system for electron emission



Nov. 17, 1936. T. w. SUKUMLYN CONTROL SYSTEM FOR ELECTRON EMISSION FiledMay 20, 1931 2 Shets-Sheet 1 W Z w A W5; fla W a my 6/ 18 jqiim Nov. 17,1936. w, SUKUMLYN 2,061,113

CONTROL SYSTEM FOR ELECTRON EMISSION Filed May 20, 1951 2 Sheets-Sheet 2Mill illlil .57 45 1 J 1 J 1 1/ 9 g g f5 f9 60 i ,4,. I 5% E V 55 g i 5/r? imgas 2 1.1M 1'1 ,Z'nyanfar 64 MEL mamas M wum/ yn Patented Nov. 17,1936 PATENT OFFICE CONTROL SYSTEM FOR. ELECTRON EMISS ION Thomas W.Sukumlyn, Los Angeles, Calif.

Application May 20, 1931, Serial No. 538,723

I Claim.

This invention relates to a system for controlling electron emission.

There are numerous applications now known for electron emission devices.Among others may be mentioned the scheme for electrically scanning animage to be transmitted for television. In such schemes, an image isfocussed on a photoelectric surface, as for example, may be formed by a.layer of sodium, potassium or other suitable compounds. Electrons areemitted from each element of this surface in accordance with theintensity of illumination reaching it. The whole area of this surfacethus projects a beam of the same cross sectional dimensions as thesurface, formed of electrons. The scanning is obtained by causingrelative movement across the beam, of a target or anode which ismaintained positive with respect to the photoelectric surface orcathode. The number of electrons reaching the target at 20 any instantthus depends upon the intensity of electron discharge from thatelemental area of the surface which is at that instant active to sendelectrons to the target.

The relative movement of the beam and target must be cyclic and so rapidthat the whole area is scanned during the period that is within theperiod of the persistence of vision; that is, so that the completescannings occur at such a frequency as to give the impression ofcontinuity. 30 This speed is of the order of one-tenth or onefifteenthof a second, which represents the time' for one complete scanning of thebeam, whereby ten or fifteen images are produced every second. Thevarying electron flow to the target is made 5. use of for varying thecurrent flowing in an output circuit, which can be reproducedsynchronously at a distant point for translating the currents into lightimpulses reassembled to form the image.

It is apparent that since each image must be subdivided into a largenumber of elements, the scanning must be extremely rapid, andappropriate amplifiers must be used to provide sufficient variations incurrent to be eiiectively transmitted. To secure the rapid scanning, ithas been proposed to secure the relative motion of the electron beam andthe target by moving the beam cyclically and leaving the targetstationary. This permits the use of electricity for the movement of thebeam, as by appropriate magnetic or electric forces. For example, acrossone direction of the beam, an electromagnetic force can be applied,alternating at a high rate and of suflicient intensity to swing the beamclear across the target; and across another transverse direction, an-

other electromotive force can be provided, alternating at a lower rateand of sufficient intensity to swing the beam along this direction clearacross the target. The resultant motion of the beam is compound, and canbe described as a 5 series of back and forth movements successively atdifferent levels until the whole beam is scanned, when the cycle isrepeated.

Definite difficulties arise in such scanning systems. For example, ahigh driving potential must 10 be used, as by the aid of a positivescreen, for impelling the electrons across the evacuated space betweenthe emitter and the target. However it has been found that emission fromthe photoelectric surface is complex in response to the 15 energizinglight. Some of the electrons proceed at such slow 'rate as never toreach the target; and others instead of proceeding in a direction normalto the surface, are oblique. These cause distortion of the reproducedimage.

It is one of the objects of my invention to make it possible to reducethis cause of distortion very materially; and more particularly by adefinite structure of the positive screen which acts either tostraighten the elemental beam from the eleas mental area, or to reducethe diverging component thereof.

It is a further object of this invention to make it tpossible to reducethe size of the transmitter tu e.

In the prior schemes of this general character, the whole beam ofelectrons is influenced by a common set of electrical influencingdevices, such as coils or condenser plates. It is apparent that theedges of the beam, nearest these devices, is influenced most, so that afurther cause of distortion is introduced. It is another object of myinvention to obviate this distortion by influencing elements of the beamseparately.

My invention possesses many other advantages, 40 and has other objectswhich may be made more easily apparent from a consideration of severalembodiments of my invention. For this purpose I have shown a few formsin the drawings accompanying and forming part of the presentspecification. I shall now proceed to describe these forms in detail,which illustrate the general principles of my invention; but it is to beunderstood that this detailed description is not to be so taken in alimiting sense, since the scope of my invention is best defined by theappended claims.

Referring to the drawings:

Figure 1 is a diagram of a system embodying one form of the invention;

system;

Figs. 6 and? are greatly enlarged detail fragmentary views of the screenused in connection with the form of the invention shown in Fig. and

tion.

In Fig. 1 there is shown an envelope or tube II which is highlyevacuated and which encloses the elements of the electronic transmitter.Thus there is a cathode l2 having a suitable photo-sensitive surfacefacing an illuminated object l3 exterior of the tube II. This object hasan image focussed on cathode i2. as by a lens system 4. The electronbeam emanating from cathode I2 is accelerated by a screen l5 (Fig. 2)which is kept at a suitable high positive potential, such as 500 volts,with respect to cathode 12. A battery l6 isindicated as supplying thissuitable potential.

A target or anode I I is disposed at the opposite end of tube II, and iskept at a suitable positive potential with respect to cathode l2, as bya battery I8. The circuit connecting anode l1 with cathode |2 also canbe connected to appropriate amplifiers l9' and to a transmission line.This target I! has an area corresponding-to an elemental portion of thebeam. In order to ensure that only one element of the beam is active atone time to pass electrons to target use can be made of an electricshutter or shield 2| of mesh form, and held at a suitable positivepotential with respect to cathode I2, as by a battery 22. This shieldcan pass the light from object I3, and has a central aperture exposingtarget Thus this shield captures all electrons except those that passdirectly to the target, and acts as an electric shutter.

The movement of the electron beam relatively to target can be effectedeither by capacity action or by electromagnetic action. In the presentinstance, there is shown apair of coils 23, 24, to affect the beammagnetically, and arranged on opposite sides of tube II, and energizedby an oscillator 25 for causing the beam to swing in a verticaldirection, say at the rate of fifteen times a second. Horizontaloscillation of the beam is similarly effected, but at a much higherrate, say five thousand times a second, by the aid of horizontallyarranged coils, energized from oscillator 26. Only one of the pair ofcoils so energized is shown at 21; but it is to be understood that'onthe other side of tube H, a similar coil energized similarly to coil 21,is provided.

Some of the electrons in the beam have a tendency to diverge from thestraight normal path; and some are emitted from cathode l2 at a lowvelocity. To keep the electrons normal and to absorb those at lowvelocity, the screen If: is made deep, as by the use of sideinterconnecting plates forming elemental areas 29, Due to the positivecharge on screen l5, and to its depth these low velocity electrons arereadily attracted thereto; and the high speed electrons are given agreater impetus inthe direction intended for them. The elemental areasor open spaces 29 of the screen are merely illustrated diagrammatically;ordi-- Fig. 8 is a diagram of a still further modificaformed by thinintersecting or honeycombed plates in an obvious manner.

Shield or shutter 2| can be also made deep, to eliminate as much aspossible, any charges on the back wall of tube The angled beam ofelectrons are thus more apt to be caught thereon instead of passingthrough the shield. The light beams from lens I4 can, however, passbecause they are substantially in line with the shield openings.

A thin metal deposit 28 inside tube H and kept at a positive potential,serves as a plate extending shield 2| to return the electrons to theoathode when the beam is angled to reach the sides of the tube.

W Furthermore, for effective operation, the tube II should be veryhighly evacuated, and the potentials of elements l5, 2|, and I1 shouldbe high, of the order of five hundred to a thousand volts, to providethe desired acceleration of the electrons. Y

Fig. 3 illustrate a form of the invention in which the length of thetransmitter tube can be reduced.

Thus in the evacuated vessel or tube 30; the cathode or photosensitivedevice 3| as well as the wide screen 32 are concave toward the target33, producing'a converging electron beam. The illuminated object 33 hasits image focused as by lens 34 onto the concave surface of cathode 3|.The beam being more restricted, can also be more readily controlled bythe devices 23, 24; 21. The shield 20'can be also deep and concave.

The idea of concentrating or straightening the electron beam byappropriate design of the screen can be carried out in other ways. Forexample, in Fig. 4, the cathode 35 emits electrons through a pair ofsets of plates 36, 31 which together form the screen. The set 36 isarranged horizontally, and set 31 is arranged vertically. Both sets arein general kept at a high positive potential with respect to cathode 35,as by the aid of battery 38. However, each set of plates includesalternate plates that are maintained positive with respect to the otherplates of the set. In other words, the plates form alternate positiveand negative elements, which can be kept at constant potenials as bybatteries 39, 39'.

As an elemental stream of electrons passes between the plates 36, thepositive plates pull the stream away from the negative plates, causingthe elemental stream to be flattened as indicated by the dotted lines40, in a horizontal direction. The angularities of these dotted linesare exaggerated for clarity, it being understood that these linesconverge on the shield 2|. Each of these fiat streams, is split up intoa series of elements by the plates 31, which act on each of the split upelements to concentrate them in a vertical direction. Thus by the actionof the two sets of plates, the electron stream is divided and againsubdivided into the desired small elements which are concentrated inboth directions, and keep them moving in a straight line. As in theprior forms described, the depth of the entire screen structure 36-31 issufficient to capture the very slow moving electrons and the greatlydeviating electrons, and ensure distortionless transmission. However,most of the electrons will here be concentrated into ,straight beamswithout absorption. r

Of course, no attempt is made to indicate a practical separation of theplates in elements 36, 31; as preferably a much larger number can beused in each set, to provide smaller elemental beams.

The successive compression of the elemental beam in two transversedirections to obtain concentrated beam elements, can also be produced bya compound shield structure, such as is illustrated in Figs. 5, 6 and 7.In this instance the cathode 4 l, shutter 42, and target 43 are arrangedsubstantially as before; as well as the scanning elements 23, 24, 21.The screen 44, however, has two series of plates of definitearrangement, which are kept positive and negative with respect to eachother.

One set of plates 45 (Fig. 6) is convoluted to form a series of bends.These plates are so arranged that the bends come opposite each other,the series of bends thus forming a series of cellular spaces orhoneycombs 41. All of these plates are kept at a potential negative withrespect to another set of plates to be described, as by a battery 46. Itis through the spaces 41 that the elemental beams of electrons travel.

Another set of plates 48 is used, which intersect the spaces 41, as bybeing spaced between adjacent plates 45. These plates are, however,insulated from plates 45, as by very thin pieces of insulation 49. Thisinsulation can be formed by a thin film of enamel, or a thin plate ofmica, or the like. All of the plates 48 are connected together, andmaintained positive with respect to plates 45, as bybattery 50.Furthermore, at the center of each space 41 formed between plates 45,the plates 48 are provided with projections 5|.

It is now possible to explain the action of the screen 44 as theelectrons progress through spaces 41 (in Fig. 6, in a direction normalto the plane of the drawings). Since plates 48 and accordinglyprojections 5| are positive With respect to plates 45, these projectionsattract the electrons, while the sides of the spaces 41, being negative,repel the electrons. The net result is that the electrons cluster nearthe projections 5| as indicated diagrammatically by the dots 52. Manyelectrons deviating from the straight normal, as well as the slow movingelectrons, will be straightened out and accelerated. Because the widthof plates 45, 48 is quite substantial, as illustrated in Figs. 5 and 7,the very slow moving electrons and those greatly deviating from normalwill be captured by plates 48.

In this form of the invention, the scanning is effected as before by thecoils 23, 24, 21, or equivalent devices. Such devices, however,influence those elemental electron beams most strongly which areadjacent the edges of the tube. In the form of my invention illustratedin Fig. 8, the elemental beams are not so discriminated against.

In this form, the evacuated tube 53 encloses the usual photoelectriccathode 54, the positive concentrating and accelerating shield 55(constructed in any of the ways heretofore described), the positiveshutter 56, and anode or target 51. The circuit connecting target 51with cathode 54 can include the appropriate amplifiers 58. Thedeflecting of the elemental beams from cathode 54 to produce thescanning effect is provided by a pair of sets of plates 59, 50. The set59 is arranged horizontally inside tube 53 and is used for swinging theelemental beams in a vertical direction. The set 60 is arrangedvertically inside tube 53 and is used for swinging the elemental beamshorizontally.

Since both sets of plates are similarly constructed, set 59 only, needbe described in detail. This set includes a series of paired plates, thenumber shown being diagrammatic and it being understood that many morecould be used in an actual embodiment, to secure a fine subdivision ofthe whole beam. The plates are alternately of opposite polarities. Inthe instance shown, the top plate and every other plate is negative,while the remaining plates are positive. The plates are in closelyadjacent pairs, providing spaces such as SI for the elemental beams topass between a pair of opposite polarity plates. The plates can be heldseparated in any desired manner as by insulation layers. 1

At the instant shown, the beams are swun downwardly in these spaces 6|as indicated by the dotted lines 62, because the top plate of each spaceis negative nd repels the electrons, while the bottom plate is positiveand attracts the electrons. However, the relative polarities change, sayat the rate of fifteen times a second, so that the beams are oscillatedat that frequency in a vertical direction. This change in polarity isaccomplished by connecting the alternate plates to opposite terminals ofa source of alternating current, such as transformer 63, fed byoscillator 6 The horizontal oscillation of the elemental beams isaccomplished at a much faster rate, as by providing the oscillator 55 of5,000 cycles, feeding transformer 66. The opposite terminals of thistransformer are connected to alternate plates of the set 60. This setoperates in a manner similar to set 59.

I claim:

1. In a system for electric scanning, a photoelectric cathode, an anode,means for causing relative movement between the beam of electronsemitted from the cathode, and the anode, and means in the path of thebeam for dividing the beam into concentrated elemental beams, saiddividing means comprising a series of electrical plates that arealternately negative and positive with respect to each other.

2. In a system of electrical scanning, a photoelectric cathode, ananode, means for causing relative movement between the beam of electronsemitted from the cathode, and the anode, and a positive screen in thepath of the beam, said screen having deep cellular spaces, the cathodeand screen being concave toward the anode.

3. In a system of electrical scanning, a photoelectric cathode, ananode, means for causing relative movement between the beam of electronsemitted from the cathode, and the anode, a series of spaced plates inthe electron stream and having alternately opposite polarities, anotherseries of similar plates but transverse to the first series, and meansfor maintaining said two series of plates positive with respect to thecathode.

4. In an electronic emission device, a cathode, an anode, and a positivescreen in the path of the electrons, and between the anode and cathode,the cathode and screen being concave toward the anode, and the screenhaving deep cellular spaces.

5. In an electronic emission device, a cathode, an anode, a series ofspaced plates in the path of the electrons and having alternatelyopposite polarities, another series of similar plates but transverse tothe first series, and means for maintaining said two series of platespositive with respect to the cathode.

6. In a system of electric scanning, a photoelectric cathode, an anode,an evacuated vessel enclosing the anode and cathode, a series of platesdefining elemental spaces and located in the vessel, and means forvarying the potentials of the plates on opposite sides of each space toswing the electron beam passing through the space.

7. In a system of electric scanning, a photoelectric cathode, an anode,an evacuated vessel enclosing the anode and cathode, a pair of series ofplates inside the vessel, one series being transverse to the other anddefining elemental spaces for the passage of electrons, and means forvarying the potentials of the plates on opposite sides of each space toswing the electron beam passing through the space.

THOMAS W. SUKUMLYN.

